1. Field of the Invention
The present invention generally relates to drive arrangements for all terrain vehicles. More specifically, the present invention relates to separated engines and final drive assemblies for use in all terrain vehicles.
2. Related Art
All terrain vehicles are constructed for use in all kinds of rough, rocky and uneven terrain. The vehicles generally comprise a frame that defines an engine compartment, an engine positioned within the engine compartments and a transmission that drives a set of wheels with power from the engine. The transmission typically is included within a transmission case that is directly connected to the engine and generally powers the rear wheels through a shaft and differential assembly. Preferably, substantial clearance is maintained between the vehicle and its associated components and the ground over which the vehicle is being operated.
In some off road vehicles, the drive wheels are independently suspended.
Independently suspended wheels allow the wheels to make contact with the ground independently of the positioning of the associated wheel. For instance, the motion of a right rear wheel is not necessarily tied to the motion of a left rear wheel. The independent suspended wheels, however, have wheel travel limitations. Wheel travel is particularly important in off road vehicles, especially with respect to independently suspended drive wheels.
In vehicles employing independently suspended drive wheels, the drive wheels are separately powered through independent half shafts. The half shafts preferably are coupled to the transmission and to the respective wheels by constant-velocity couplings. While the vehicle is running, the suspensions absorb shocks and impacts from the ground. Thus, the wheels move in a vertical direction relative to a frame of the vehicle. As the wheels bounce up and down, the drive shafts pivot with respect to the transmission. The pivoting causes a change in a crossing angle defined by a center of the constant-velocity coupling and the center of the drive shaft.
By increasing the available travel of the wheels independent of the other, operation of the vehicle is improved. For instance, the suspension system is better able to absorb the impact caused by sudden jolts or large bumps. In addition, the suspended wheel is better able to remain in contact with the ground. To increase the wheel travel, either the crossing angle or the length of the half shaft should be increased.
It has been discovered that increasing the crossing angle yields some undesirable results. For instance, by increasing the crossing angle, the joint is subjected to extreme wear. In addition, the joint is more likely to be damaged as the joint is reconfigured to expand the limits of the crossing angle.
Accordingly, the present invention increases the length of the half shafts; however, rather than simply increasing a lateral dimension of the vehicle to accommodate a pair of longer half shafts, the constant-velocity couplings have been reconfigured to reduce a lateral dimension of the pair of couplings. A variety of advantages stem from the changes, as will become apparent from the following detailed description.
Desirably, the improved transmission features a pair of constant-velocity couplings that have been integrated into a single housing. The housing desirably reduces the lateral dimension associated with the pair of couplings. In addition, the housing allows a reduced distance between the moving components that are positioned within the housing. The reduced distance and the reduced lateral dimension allows the length of each half shaft to be increased. Thus, while the crossing angle is minimized, the increased half shaft length results in increased wheel travel. The reduced crossing angle better protects the coupling. Moreover, the increased wheel travel improves vehicle performance. Furthermore, even through the half shaft length is increased, the overall width of the vehicle can remain the same or be decreased.
Accordingly, one aspect of the present invention involves an all terrain vehicle comprising a frame. A right wheel and a left wheel are independently mounted to the frame. An engine compartment is defined within the frame and an engine is mounted within the engine compartment. The engine drives the right wheel and the left wheel through a transmission. A right drive shaft connects the right wheel to the transmission and a left drive shaft connects the left wheel to the transmission. The right drive shaft and the left drive shaft are linked to the transmission through an output arrangement. The output arrangement includes a gear portion and a housing portion. The housing portion includes a left bore and a right bore. A left cage is positioned within the left bore and a right cage is positioned within the right bore. A left inner member is positioned within the left cage and a right inner member is positioned within the right cage. A proximal end of the left drive shaft is secured for rotation with the left inner member and a proximal end of the right drive shaft is secured for rotation with the right inner member. The left cage is secured for rotation with the housing portion and the right cage is secured for rotation with the housing portion. The left inner member is secured for rotation with the left cage and the right inner member is secured for rotation with the right cage.
Another aspect of the present invention involves a constant velocity coupling comprising a housing. The housing comprises a cylindrical body, a ring gear extending about an exterior surface of the cylindrical body, a first axial bore extending into the cylindrical body and a second axial bore extending into the cylindrical body. The first axial bore and the second axial bore both have centerlines that are aligned with a centerline of the cylindrical body. A first cage is positioned within the first bore and is coupled for rotation with the cylindrical body. A second cage is positioned within the second bore and is coupled for rotation with the cylindrical body. A first half shaft is coupled to the first cage for rotation with the first cage and a second half shaft is coupled to the second cage for rotation with the second case.